The present invention relates to a method for fabricating a semiconductor device, and particularly to a method for forming a barrier metal layer and a metal layer on the surface of a contact hole formed on a semiconductor device.
Conventionally, a known method called "sputtering" is used for depositing metal on the surface of the contact hole formed on the semiconductor substrate so as to form the metal layer. In this case, however, a step coverage around the contact hole becomes worse, resulting in increase of a contact resistance.
A proposed process to solve the foregoing problem is to deposit aluminum on the surface of the contact hole and thereafter anneal the semiconductor device, or deposit aluminum while heating the semiconductor substrate. Accordingly, the contact resistance is reduced by burying the contact hole in the manner of the above process. Silicon component is, however, extracted from the semiconductor substrate and stacked in a lower portion of the contact hole, so that a contact area between the metal layer and a diffusion layer under the contact hole layers is reduced.
To prevent the silicon extraction phenomenon stated above, a distribution layer which is aluminum alloyed with copper of about 0.5% is formed. Accordingly, the silicon extraction phenomenon can be considerably reduced by not supplying silicon component to the aluminum. However, since the silicon component is not included in the aluminum, silicon component contained in the substrate is rapidly melted into the aluminum until the silicon component reaches a critical melting point, forming the void in the portion where the silicon component of the substrate flows out into the aluminum, and the aluminum flows into the void formed in the substrate, thereby causing aluminum spiking at the portion where the silicon component is missing, which increases a leakage current.